There are 3 basic types of Attack Craft: Fighters, Bombers and Assault Boats.
New Ship Components:
Hangar Bay: Can launch 1 Squadron per Strategic Turn, can store 6 Squadrons. I have to look it up, but the Space will be the same as a Macro Cannon Battery as they would replace them. Will Edit tonight.

A Squadron represents 4 individual Attack Craft. Each craft is 1 Strength but the Squadron attacks as one unit, so a Squadron on a bombing run which has lost two Bombers would be Strength 2.

Squadrons may make 180 degree turns and are subject to all the piloting rolls normal ships are. Bombers and Assault Boats may make 1 attack, Fighters may make 3, after which they must return to their mothership for refuelling/rearming. Landing is a Routine (+10) Piloting Test. Failing the test is…bad. We'll figure out an entertaining chart for that later.

Combat

Damage: For most purposes, Attack Craft have 1 Hull Point, meaning any successful hit will take them out. If you wish (I do) we can make an entertaining chart with more detailed damage results. For most encounters the pilots will be NPC's and whether the ship is destroyed or has to limp back to base is inconsequential, but for salvage purposes roll a d10 for each "destroyed" Craft. 1-6 the Craft is destroyed, 7-10, the ship is damaged and can be salvaged.
Fighters Vs. Attack Craft:
At any time a Fighter Squadron comes within 1 VU of an enemy Squadron, the attacker may either make an attack and veer off, or commence a dogfight. Dogfighting places the attacking squadron within base contact of the enemy and it will move with the enemy until it makes 3 attacks, runs out of munitions and disengages, or one of the squadrons is destroyed. An opposed role is made for each Squadron, (Piloting + BS) vs. (Piloting + Dodge). The attacker destroys one enemy per level of success. Alternatively, separate rolls can be made if one or more of the pilots is a PC or important NPC with higher skills than the standard pilot.

Fighters Vs. Ships:
Fighters, due to their miniscule damage, cannot penetrate Void Shields, and can only substantially damage the smallest and weakest armored ships. They can, however make a run versus a ships Turrets. Usually, this is done in waves to prepare for a successful run by Bomber Squadrons. For every level of success, reduce the Turret's BS by 2 temporarily for the remainder of this and the next strategic turn.
Bombers and Assault Boats Vs. Attack Craft:
Similar to Fighters, but due to their weaker armament they suffer -15 to their Gunner's BS. Truly, Bombers and Assault Boats rely on their own Fighters for protection.Bombers Vs. Ships:

Bomber Squadrons leave their Motherships with orders to target a specific known component. Once inside the enemy's Void Shields they drop their payloads of Melta and Plasma bombs to devastating effect. Resolve hits against the target as normal.
Assault Boats Vs. Ships:
I haven't quite worked this one out, but each Assault Boat that makes base-to-base contact with an enemy ship carries out an immediate Hit-and-Run attack. In BFG, there is no provision for getting back on the thing and making it home again…

Ships Vs. Assault Craft:
Ships may fire at Squadrons with their main armament provided the Squadron is over 2 VU away. The Craft are small, fast and hard to hit, so the Ballistics test is Difficult (-20) with each level of success knocking out 1 Assault Craft. For example, a Macro Cannon battery would have to score 4 levels of success to wipe out an entire squadron in one shot.
Turrets: Turrets get one attack at each Squadron that comes within range (1 VU) per Strategic Turn. It's a straight-up Ballistics test and each level of success knocks out 1 Assault Craft. So, if 3 Squadrons of Bombers rake a Lunar Class Cruiser, the Cruiser gets 2 shots at each Squadron, since it has a Turret Rating of 2. A lesser craft with no Turrets, could possibly suffer up to 12 1d10 hits with a very low crit rating…ouch. Craft piloted by a PC are allowed a Piloting+Dodge test (+0) to avoid damage.

On Movement:
If you're using visual representations, there are 3 good ways to do this. The important thing is space is a big place and each Squadron should be considered to occupy the same VU.
Mini's: If you have Assault Craft minis, it looks more impressive to move four of them per Squadron, but they have to be in base contact and because most bases are about 1 VU wide, you should consider them all to actually occupy the space under the "Lead Ship". It does make it easy to keep track of Squadron Damage as you simply remove a model as it is destroyed.
Abstract Minis: Alternatively, you could use 1 model to represent the entire Squadron and use a d4 to keep track of Squadron losses.
Counters: There are counters representing Squadrons in the BFG material over at GW's Specialist site. They work just fine and it's a free download.
Fighters
Fury (Imperial) +3 BS, +3 Maneuverability
Barracuda (Tau) +5 BS,
Swiftdeath (Chaos) +1 Move, +3 Maneuverability
Darkstar (Eldar) 5 attacks available instead of 3
Ork Fighta-Bommas 2 attacks total, d10, Crit Rate: 3, no "Bomber penalty" for dogfighting.